The objective of the proposed research is to devise and perform psychophysical experiments giving information as to the nature of the receptor characteristics in color defective observers. The particular studies which are relevant to these objectives include: 1) spectral sensitivity and luminosity, 2) color mixture data, 3) Stiles-Crawford effect in dichromats and monochromats, 4) hue estimation in anomalous trichromats, and 5) perceptual latency in normal and anomalous trichromats. Current theoretical interests include delineating the shape, position and optical density of the visual pigments, the variability of color mixture data, the roles of neural versus photochemical factors in various psychophysical tasks, the nature of the luminosity curve, and the Stiles-Crawford effect. BIBLIOGRAPHIC REFERENCE: Spectral sensitivity of the foveal cone photopigments between 400 nm and 500 nm (Smith, V.C. and Pokorny, J.) Vision Research 15:161, 1975.